The decorative illumination of aquariums has been widely used, often employing simple heating lamps or fluorescent lamps accommodated above water. These techniques are disclosed, for example, in U.S. Pat. Nos. 3,908,598; 4,516,529; and 5,353,746. However, it was found that the bright illumination produced by these lamps could cause damage to some kinds of aquarium fish, affect their natural colors, and may cause the discoloration of various colored elements in the aquarium.
There is a great variety of systems utilizing standard lamps for underwater illumination. Unfortunately, these systems are bulky, owing to the unavoidable requirement for a suitable means to prevent the penetration of water into the regions of electrical contacts. This makes such systems unsuitable for decorative illumination.
Illumination systems based on LEDs have been developed, being disclosed, for example, in U.S. Pat. Nos. 5,211,469 and 5,948,837. Notwithstanding the fact that these systems are more miniature than those based on the standard lamps, they suffer from the point-like nature and non-isotropic illumination of LEDs. Additionally, the use of LEDs requires electrical contacts to be located under water which, in turn requires the provision of a special means for preventing water from penetrating the contact region.
Systems for decorative illumination of aquariums utilizing optical fibers as light sources have been developed, and are disclosed, for example, in U.S. Pat. Nos. 3,749,901; 3,609,343; 5,067,059 and 5,546,289. These systems suffer from the drawback associated with the need for a bulky assembly aimed at inputting light into the optical fibers. Such an assembly typically comprises an external light source (i.e., lamp), a drive for rotating spectral filters, etc. Additionally, optical fibers are not sufficiently flexible, and provide the entire radiation output at the butt of the fibers only, that actually make them point-like light sources.